DMR seems to be the consensus among the MLG players who got the game early and have been playing since it was still being tested. I agree as well, you get better range on the DMR and because it's single shot you don't have to worry about missing any of the bursted bullets.

How is MLG playing this game (as far as weapons, ordinance, tac packages, etc) ? Seems very un-MLG-like.

From the stream I saw before the game was released, a lot of them were using jetpack and pro vision because they are the most powerful abilities in the game. Other than dexterity, I didn't see what other perks they were using. They were definitely using ordnance as well. It's possible that Microsoft requested they use all the new stuff for the pre-release coverage, though. I imagine a lot of this will change later down the road.

Actually, I've seen quite a few pros (Walshy, Bravo) calling for MLG to not summarily dismiss load-outs and personal ordnance. I think they're mostly enjoying this game and they'd like to see it stay intact this time. There's also the whole "Joe Schmoe would rather see pros play the same game he is playing, just on a higher level" argument.
My load-outs all use DMR (I am in love with the new DMR) and plasma pistol (uses: anti-vehicle, occasional noob combo). My straightforward load-out is just frags, Promethean Vision, Shielding (faster recharge), and Dexterity (faster reload). I'm playing around with different perks (sorry, I'm not going to try and call them whatever 343i does, they're perks). For example, camo with faster armor ability regeneration and one or the other of the radar enhancements. I also have one I'm calling Scavenger (I still use Promethean Vision with that one, but the perks allow me to pick up fallen grenades and start with more ammo).
I may start playing around with the Light Rifle a bit, but it's going to be hard to go without my DMR.
The thruster pack could really use some tweaking - it's almost perfect in Campaign, but in Multiplayer, it's downright worthless.